1. Introduction
When studied on the basis of morphological classification, microorganisms are of many types. However, when considered from the view point of essential elements that compose cells, microorganisms are of fewer types. There is a total of 11 kinds of major essential elements that compose microbial cells: 6 organic elements (C, N, P, S, O, and H); and 5 electrolytic elements (Na, K, Ca, Mg, and Cl) are most probably contained in all microorganisms. In addition to these essential elements, it is known that, from among 9 basic trace elements (V, Mo, Se, Mn, Fe, Co, Ni, Cu, and Zn), 2 elements (V and Mo) are contained in specific microbial species, while the remaining 7 elements are contained by almost all microorganisms. Moreover, any specific microbial species contains or does not contain at least one of 3 general trace elements (W, Si, and Sn).
2. Essential Element
Whether or not an element is essential for an organism can be revealed by a method that involves examining the amount of an element to be supplied and a biological reaction, which indicates whether the element is essential for the organism, for example. Specifically, by using the method and technique determination is made that an element is essential for an organism, when the supply of the element is gradually increased from null, then the resulting biological reactions appear within a dose range in as per the following order: no growth, weak growth or nutritional deficiency, accelerated growth, optimum growth, poor growth, presence of harmful symptoms, and impossibility in growth or death. Specifically, under a particular growth environment, for example, suppose that Zn within a low-concentration range has the effect of delaying mouse growth. Zn, when given in a concentration that is slightly higher than such concentration range, promotes the growth in an accelerated manner, but Zn in an even higher concentration has an inhibitory effect, then, Zn would be regarded as an essential element for mice. These results are considered to be nutritional evidence indicating that the relevant element is essential.
3. Non-Essential Elements Contained in General Microorganisms are Reported as Below.
3-1. (V, Mo)
The element vanadium (V) has been proven to be an essential element for rats and chicks (Non-patent Literature 1). It is also known that vanadium is present at a particularly high concentration in blood cells of sea squirts. However, the origin of “V” in sea squirts, the assimilation mechanism thereof, and the role thereof remain unclear. It is also known that molybdenum-containing hydroxylase is present in many biological species ranging from bacteria to humans (Non-patent Literature 2).
Higher plants do not have their own capacity for using nitrogen in the air. The supply of ammonia or a nitric acid group depends on the microbial capacity for fixing nitrogen. A nitrogenase enzyme that is responsible for a reaction that generates ammonia from nitrogen in air, which is an important stage of microbial nitrogen fixation, is a metal enzyme containing V or Mo. Hence, nitrogen-fixing microbial cells contain V or Mo (Non-patent Literature 3-6). Whether a microorganism contains V or Mo differs depending on microbial species.
Examples of nitrogen-fixing bacteria include a dozen species of anaerobic or aerobic heterotrophic bacteria (e.g., Azotobacter sp., Clostridium sp., Desulfovibrio sp., Escherichia sp., and Klebsiella sp.), root nodule bacteria, Rhizobium sp., a symbiont living with leguminous plants, photosynthetic bacteria, and about 40 species of blue-green algae. Among approximately so-called a hundred thousand species of microorganisms, the number of species of nitrogen-fixing bacteria is limited, but they are broadly distributed on earth. When these nitrogen-fixing bacteria are grown under nitrogen fixation conditions, V and Mo are essential elements, but are not essential elements when the nitrogen-fixing bacteria are grown under heterotrophic conditions.
Meanwhile, a haloperoxidase enzyme, by which a reaction is conducted to degrade C-halogen bonding among limited species of mushrooms and fungi, is a metal enzyme containing V.
3-2. (Si)
Among microorganisms in broad terms (including bacteria, yeast, filamentous fungi, basidiomycetes and algae, and Protozoa), a type of algae needs Si. Diatoms contain Si as a constituent of cell walls, and thus Si is essential (Non-patent Literature 7). Si is also found in some kinds of Radiolarida. However, the need of Si has not been proven for general microorganisms (bacteria, yeast, filamentous fungi, and basidiomycetes) other than algae and diatoms.
Moreover, several microorganisms have been tested for the capacity for metabolizing an organic silicon compound or an organic silicone. As a result, it has been found that relatively many filamentous fungi and bacteria metabolize such an organic silicic acid compound (Non-patent Literature 8). It has also been found that a strain of Bacillus sp. is capable of eluting a phosphate group from a phosphorus ore (Non-patent Literature 9). In this case, microbial cells contain Si. However, although microorganisms degrade and metabolize organic carbon portions, their assimilation of silicon has never been reported. It is rather assumed that inorganic silicon is finally generated.
3-3. (Ge)
Ge-containing yeast cells were prepared (Patent Literature 1). In this literature, yeast was caused to incorporate Ge in a nutrient-rich medium. The literature describes that the Ge compound was incidentally incorporated by yeast with low incorporation efficiency and does not describe that such incorporation can be achieved by other microorganisms.
3-4. (Te)
It has been reported that filamentous fungi having natural resistance to a Te compound were caused to incorporate Te. Although Te was used for the filamentous fungi of this literature under conditions of a limited amount of an S source, the aforementioned literature does not report that Te can be used as an S source, P source, N source, or C source substitute in wide-ranging general microorganisms.
3-5. (Metal Adsorption by Microorganism)
As a result of studies to cause microorganisms to adsorb hazardous metals including Cr, Cd, Hg, and Pb in order to eliminate these metals, it has been found that many microorganisms adsorb various metals, as reported in Patent Literature 2, for example. For example, it has been reported that Pb was bound to cell membranes or outer membrane polysaccharides, and that when incorporation of lead citrate was attempted, its citric acid portion was metabolized as a nutrient, but Pb was bound to and deposited on cell surface layers.
3-6. (Conclusion)
As described above, a few facts indicating that microorganisms incorporate non-essential elements have been reported. These facts are characterized as follows.    1. Subject non-essential elements include highly toxic elements and the number of types thereof are limited to few.    2. Microorganisms used herein are a small number of specific microorganisms. These microorganisms were newly isolated from nature as microorganisms capable of incorporating compounds that contain elements of interest, or were selected from many existing microorganisms. It has not been described about whether or not microorganisms other than these selected strains could incorporate the elements of interest.    3. A case, in which a method for culturing microorganisms is improved for the purpose of causing them to incorporate safe or low-toxic non-essential elements, has never been reported. It has also never been reported that a microorganism can be modified by mutation or the like to make it possible to efficiently incorporate such elements.